Family Resemblance

Even though they are members of a cognitive category, it is very often the case that not a single feature shared with every member of the category exists. Rather, a member of a cognitive category is similar with another member in many features, and again, that member shares many features with another member, and so forth. It is not important whether there exist features shared with every member of the category: a member shares many features with neighbors, and they with their neighbors. These linkages make them a member of a category.

Faces of members of a family are similar, but a feature they have in common dose not necessarily exist.

So, we call such phenomena caught in relations among members of a category, the Family Resemblance Effect after Rudwig Wittgenstein.